Pseudo-separation for phenylalanine (Phe), ibuprofen (Ibu), capsaicin (Cap) and norfloxacin (Nor) were studied by sodium dodecyl sulfate (SDS) or hydroxypropyl-β-cyclodextrin (HPβCD) assisted diffusion ordered spectroscopy (DOSY). Stokes-Einstein equation shows a linear relationship between the logarithms of apparent di?usion coe?cients and logarithms of molecular weight (Mw). However, with matrix added, block factors became the important factors than molecular weight. Pseudo-separation was improved by SDS or HPβCD assist. Research showed different separation mechanism for SDS and HPβCD-assisted DOSY. The former used different lipo-hydro partition coefficient, and the latter used complexing mechanism.